The fast transfer modes (PIO modes 3 and 4, multiword DMA modes 1 and 2)
are the cornerstones of Fast-ATA and EIDE. These are marketing terms
contrived by disk drive manufacturers. Enhanced IDE is a Western Digital
trademark; Fast-ATA is a term coined by Seagate, and endorsed by Seagate
and Quantum.
EIDE consists of:
- Fast transfer modes: PIO mode 3 or better, multiword DMA mode 1 or better,
- LBA mode (explained in section
10.7
),
- Four devices on the ATA interface: secondary port,
- No 504MB limit with DOS: WD Enhanced BIOS,
- tape backup and CD-ROM devices on the ATA interface: ATAPI.
Fast-ATA and Fast-ATA-2 embrace:
- PIO mode 3 (and 4 for Fast-ATA-2), multiword DMA mode 1 (and 2 for Fast-ATA-2),
- Read/Write multiple commands (also known as block mode; see
Q
10.6
),
- LBA mode.
The difference between the two schemes is mainly in the scope of
EIDE. Hardware can be tagged 'EIDE' even if only part of the EIDE
feature set has been implemented, which can lead to some confusion.
This FAQ will avoid the term EIDE whenever possible, discussing its
component parts (ATA-2, ATAPI, etc) instead. This allows you to see
exactly what 'EIDE' features you need in your specific situation.
Very true, unfortunately.
This FAQ doesn't really deal with specific interfaces, but two very
popular interface chips have been shown to contain bugs too serious to
ignore:
- the CMD640x, a dual-channel PCI to EIDE interface used on many
mainboards (Intel!) and interface boards, has a number of dangerous bugs
you need to be aware of.
- The PC-Tech RZ-1000, used on AT&T, Dell, Gateway and Intel
boards, also has two data-corrupting bugs. See also
http://www.intel.com/procs/support/rz1000/index.htm
.
In both cases, the corruption occurs only in specific software
environments and is very subtle; you can go on working for months without
suspecting anything more than buggy software. The damage can be
immense. For all the details, look at Roedy Green's (
roedy@bix.com
) "PCI EIDE controller
flaws" FAQ included with his
EIDE test
program which will
test your system for the bugs.
BE WARNED that you're playing Russian roulette with your data if you
continue working on an affected machine without taking notice of this
problem.
The word "mega" is an ISO prefix designating a factor 1,000,000. A proper
megabyte is 1,000,000 bytes. Because computers use binary technology
and like working with powers of two, 2ˆ20 bytes, that is 1048576 bytes, is
also usually referred to as a megabyte.
Which of the two types of megabyte you're dealing with depends on the
context. For storage devices, a megabyte usually means 1,000,000
bytes. Some software uses "binary" megabytes, though, and will show a
smaller capacity than the drive label says! This includes most BIOSes.
This FAQ uses megabytes of 1048576 bytes throughout.
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